This invention relates to foul release coatings and articles coated therewith. More particularly, it relates to sprayable foul release coatings which may be employed without undue environmental harm.
As poetically stated in U.S. Pat. No. 4,861,670, "Marine fouling due to pernicious and pestiferous sessile organisms is a problem which reaches from ancient times to the present." In more simple terms, a perennial major aggravation to shippers and users of marine equipment in contact with water is the tendency of such equipment to become encrusted with various varieties of wildlife, as illustrated by barnacles and zebra mussels.
Said patent goes on to describe in considerable detail the types of treatments that have been employed, starting as early as 1854, to minimize marine fouling. Treatment materials have included compounds of such metals as copper, tin, arsenic, mercury, zinc, lead, antimony, silver and iron, as well as toxic organic materials such as strychnine and atropine. With increasing interest in the state of the environment, the use of such materials has been strongly discouraged.
More recently, polyorganosiloxanes (hereinafter sometimes designated "silicones" for brevity) have been found useful as anti-fouling coatings. They include condensation cured room temperature vulcanizable (hereinafter sometimes "RTV") compositions comprising silica as a filler in combination with silanol-terminated or di- or trialkoxy-terminated silicones, catalysts and crosslinking agents. These condensation cured compositions are typically thixotropic and are thus incapable as prepared of application by spraying. They can generally only be conveniently applied neat by such time-honored but tedious methods as brushing or roller coating.
The only potential way to make such materials sprayable is to dilute them with solvents, typically volatile organic compounds such as hydrocarbons which present their own environmental hazards. In any event, many localities have enacted legislation limiting the proportions of volatile organic compounds in such compositions to values in the parts-per-million range, far below those that would be necessary for them to serve as solvents.
British published application 2,287,248 and copending, commonly owned application Ser. No. 08/646,646 disclose silica-silicone oil masterbatches and their use in the formulation of room temperature vulcanizable silicone compositions. Said compositions as disclosed therein are, however, very viscous, having viscosities under ambient conditions as disclosed of at least 24,000 centipoise and often much higher. Thus, they similarly cannot be applied by spraying without employment of solvents.
Thus, the development of sprayable, environmentally harmless condensation curable silicone foul release coating compositions remains a concern.